Kinect tutorial 1: First steps

This series of tutorials will explain the usage of a Kinect device for “serious” researching purposes. As you may know, Kinect is in fact an affordable depth sensor, developed with technology from PrimeSense, based on infrarred structured light method. It also has a common camera (which makes it a RGB-D device), a microphone and a motorized pivot. Its use is not limited to playing with a Xbox360 console, you can plug it to a computer and use it like any other sensor. Many open-source drivers and frameworks are available.

Since its release on November 2010, it has gained a lot of popularity, specially among the scientific community. Many researches have procured themselves one because, despite the low cost (about 150 €), it has proven to be a powerful solution for depth sensing projects. Current investigations focus on real-time surface mapping, object recognition and tracking, and localization. Impressive results (like the KinectFusionproject from Microsoft) are already possible.

I will explain the installation and usage of one of these Kinect devices with a common PC, and the possibilities it offers. I will do it in an easy to understand way, intended for students that have just acquired it and want to start from scratch.

NOTE: The tutorials are written for Linux platforms. Also, 64-bit versions seem to work better than 32-bit.

Requirements

You will need the following:

A common Kinect device, out of the box. You can buy it in your local electronics shop, or online. It also includes a free copy of Kinect Adventures, which is useless if you do not own the console. Microsoft has released a Kinect for Windows device, which is a normal looking Kinect no longer compatible with Xbox360, that will only work with their officialSDK, intended for developers only.

NOTE: Kinect for Windows may have problems working with open source drivers on Linux .

Connecting everything

Kinect does not work with a common USB port. Its power consumption is a bit higher because of the motor, so Microsoft came up with a connector that combines USB and power supply. Old Xbox 360 models needed a special adapter, new ones already have this new port. Luckily, Kinect comes with the official adapter out of the box (otherwise you will have to buy one).

Just plug the adapter to any power socket, and the USB to your computer. Let’s check typing this in a terminal:

Installing the software

There is more than one way to get your Kinect working on your PC, and start developing applications for it:

Kinect for Windows: released on June 16, 2011 as a non-commercial SDK intended for application development. Version 1.5 was released on May 21, 2012. Because it comes from Microsoft, it is obviously the easiest way to get everything working. Sadly, there is no Linux version.

libfreenect library: from the OpenKinect project, it is intended to be a free and open source alternative to the official drivers. libfreenect is used by projects like ofxKinect, an addon for the openFrameworks toolkit that runs on Linux and OS X. ofxKinect packs a nice example application to show the RGB and point cloud taken from Kinect.

PrimeSense drivers: they were released as open source after the the OpenNI project was created, along with the motion tracking middleware, NITE. NI stands for Natural Interaction, and the project tries to enforce a common standard for human input using Kinect-like sensors. These official drivers are used by ROS (the Robot Operating System, a massive collection of libraries and tools for robotic researchers) and PCL (the Point Cloud Library, with everything needed for 3D point cloud processing).

SensorKinect: a modified version of the official PrimeSense drivers, used for example by ofxOpenNI (another openFrameworks addon).

For this tutorial, we are going to use PCL.

Precompiled PCL for Ubuntu

There is a PPA (Personal Package Archive, a private repository) which has everything we need. Add it to your sources, and install everything:

Compiling PCL from source

For Linuxes without a precompiled version of PCL, you will need to compile it yourself. This has an advantage, actually: you can customize the build options and choose what you want. Also, the result binaries and libraries should be a bit faster. The instructions are here, but the steps are easy so I will show them to you.

First, you must choose whether to install the stable or the experimental branch of PCL. The stable branch is the latest official release and it is guaranteed to work without problems. The experimental branch may give you a compiling error seldomly, but you can find some interesting features that stable users will have to wait some months for. Apart from that, both are built the same way.

Installing the dependencies

Some of PCL dependencies can be installed via the package manager. Others will require additional work.

OpenNI

PCL uses OpenNI and the PrimeSense drivers to get data from Kinect. It is optional, but it would not make much sense not to install it, would it? If you are using Ubuntu, add the PPA and install openni-dev and ps-engine. Otherwise, go to the OpenNI download page and get the OpenNI and PrimeSense Sensor sources. Extract them, and install the dependencies:

You are not done yet. OpenNI requires Sun’s official JDK (Java Development Kit), which is no longer available on apt repositories. Go to the Java SE downloads page (SE means Standard Edition) and download the latest version (i.e., jdk-7u10-linux-x64.tar.gz). Extract it, then move the contents to /usr/lib/jvm/ so it is available system-wide:

Sun’s JDK is now installed. You can now go to the directory where you extracted OpenNI (OpenNI-OpenNI-3d355ac/ for me), and open a terminal in the Platform/Linux/CreateRedist/subdirectory. Issue:

./RedistMaker

When it finishes, and if there are no errors, go to Platform/Linux/Redist/OpenNI-Bin-Dev-Linux-x64-v1.5.2.23/ (or your equivalent), and install (you must be root):

sudo ./install.sh

Now, go to the directory where you extracted the PrimeSense drivers (PrimeSense-Sensor-fc51d0a/ for me), and repeat the exact same procedure (go to Platform/Linux/CreateRedist/, issue ./RedistMaker, go to Platform/Linux/Redist/Sensor-Bin-Linux-x64-v5.1.0.41/, issue sudo ./install.sh). Congratulations, you have now installed OpenNI.

CUDA

Like OpenNI, nVidia CUDA is an optional dependency, that will allow PCL to use your GPU (Graphics Processing Unit, that is, your graphics card) for certain computations. This is mandatory for tools like KinFu (do not bother unless you have at least a series 400 card with 1.5 GB of VRAM).

Go to the CUDA download page, which is self-explanatory, and get the toolkit and the SDK for your system (the drivers you already have installed, right?). Give them execute permissions:

Compiling

Go the the PCL source directory (PCL-1.6.0-Source/ or PCL-trunk-Source/ for me), and create a new subdirectory to keep the build files in:

mkdir build
cd build

Now it is time to configure the project using CMake. We will tell it to build in Release (fully optimized, no debug capabilities) mode now, and customize the rest of the options later:

cmake -DCMAKE_BUILD_TYPE=Release ..

CMake should be able to find every dependency, thus being able to build every subsystem except for the ones marked as “Disabled by default”. If you are happy, you can build now, otherwise let’s invoke CMake’s curses interface to change a couple of things (mind the final dot):

ccmake .

Interface of ccmake.

Here you can change the build options. The program usage can be found at the bottom of the screen. Try turning all functionality “ON”. The most important thing, in case you want to use CUDA, is to enable it and give CMake the path to your SDK. Go to the “CUDA_SDK_ROOT_DIR” option and enter the correct path (mine was /home/me/NVIDIA_GPU_Computing_SDK/).

When you are done, press C to configure and G to generate and exit the tool. Sometimes, the options you change can activate previously omitted parameters, or prompt some warning text. Just press E when you are finished reading the message, and keep pressing C until it lets you generate (new parameters will be marked with an asterisk, so you can check them and decide whether or not you want further customization).

If you are done configuring, it is time to build:

make

NOTE: Additionally, you can append the parameter -jX to speed up the compilation, X being the number of cores or processors of your PC, plus one.

Remember that, at any time, you can manually force the project to be reconfigured and built from scratch by emptying the build/ directory with:

rm -rf ./*

Installing

It will take some time to compile PCL (up to a few hours if your PC is not powerful enough). When it is finished, install it system-wide with:

sudo make install

And you should reboot and proceed to the next section, to see if your computer now recognizes (and uses) your Kinect device.

Testing

We are going to write a simple example program that will fetch data from the Kinect and present it to the user, using the PCL library. It will also allow to save the current frame (as point cloud) to disk. So, create a new directory anywhere in your hard disk.

CMakeLists.txt

Inside that directory, create a new text file named CMakeLists.txt. PCL-based programs use the CMake build system, too. Open it with any editor and paste the following content:

CMake syntax is quite self-explanatory. We ask for a CMake version 2.8 installation, minimum. We declare a new project named “kinect_PCL_viewer”. We tell CMake to check for the presence of PCL library development files, version 1.6. If our system can not meet the CMake and PCL version requirement, the process will fail.

Next, we feed the compiler and linker the directories where PCL includes and libraries can be found, and the defined symbols. We tell CMake to use the “Release” build type, which will activate certain optimizations depending on the compiler we use. Other build types are available, like “Debug”, “MinSizeRel”, and “RelWithDebInfo”.

Finally, we create a variable, “kinectpclviewer_SRC”, that will store a list of files to be compiled (though we will only have one). We create a new binary to be compiled from these source files, and we link it with the PCL library.

Compiling

Follow the same steps you used to build PCL. That is, create a new build/ subdirectory next to the src/ one. Open a terminal there and issue:

cmake -DCMAKE_BUILD_TYPE=Release ..
make

Executing

Still from the same terminal, run the compiled example program:

./kinectPCLviewer

After some seconds, the main window will appear and the application will start grabbing frames from the Kinect. You can inspect the current point cloud using the mouse, holding the left button to rotate, the right one to zoom, and the middle one to pan the camera around. See the PCLVisualizer tutorial for additional controls and features.

Whenever you feel ready, press the SPACE key. The program will pause for a fraction of a second and the output “Saved inputCloud0.pcd.” will appear on the console. Check the current folder to see that file inputCloud0.pcd has indeed been written. You can now close the program with Q or Alt+F4.

Next, run it again giving the following parameter:

./kinectPCLviewer -v inputCloud0.pcd

This will tell the program not to take data from the Kinect device, but from the saved point cloud file instead. After it loads, you will realize that you are presented the same scene you saved to disk.

NOTE: PCD data is saved relative to the sensor. No matter how much you have manipulated the view, it will reset to default when you load the file.

Conclusions

At this point, your Kinect device should be working and getting depth data for you. There is a collection of excellent tutorials for PCL in the official webpage. I encourage you to finish them all before proceeding your experiments with the Kinect sensor.